In long-term evolution (LTE) communications, when the user equipment (UE) is in the idle state, i.e. not communicating with the LTE network, the UE's location is known to the LTE network on a tracking area (TA) level. An operator may define any number of base stations of the LTE network, known as evolved Node Bs (eNodeB or eNB for short), as belonging to a particular TA. In short, each eNB and its corresponding coverage area (i.e. cell) is configured with a particular TA at the network deployment stage. Each TA can consist of multiple cells and is defined as a group of cells (or a single cell) which the mobility management entity (MME) may use to locate the UE.
Each TA has a unique tracking area identity (TAI) consisting of the public landline mobile network identity (PLMN-ID) and the TA code (TAC). Cells which are grouped into the same TA are identified in the system broadcast parameters by a TAI. When registering with the network, the UE receives a TAI list. The TAI list includes the TAs for which the UE does not need to perform tracking area update (TAU) procedures. If a TA is not on the TAI list, however, the UE needs to perform a TAU procedure in order to inform the MME of its new location upon reselecting to the new cell.
In a dual subscriber identity model (SIM) platform utilizing a single shared transmitter, this may prove to be problematic whenever one SIM is in idle mode in LTE and the other SIM is actively operating in any other mode using the transmitter (i.e. 2G, 3G, LTE, etc.), e.g. a voice call. Because an LTE uplink transmission is required for TAU and there is only one transmitter available for the UE, the active communication (e.g. voice call) may be interrupted in order for the UE to perform the TAU procedure because the TAU procedure is prioritized for the UE to successfully receive paging from the network.
Furthermore, multiple TAUs may be performed during UE mobility. Because of the prioritization to perform the TAUs on one of the SIMs in a dual-SIM, single transmitter UE, there may be negative impact on an active communication of the second SIM such as: loss of uplink transmission as the LTE uplink transmission degrades the quality of active communications, more retransmissions leading to increased power consumption, and signaling packet loss resulting in active call drop or connection release for the second SIM.